linux-kernel - Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

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Date:	Wed, 22 Aug 2012 14:46:49 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:	tony.luck@...el.com, andi@...stfloor.org, bp@...64.org,
	gong.chen@...ux.intel.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	linux-edac@...r.kernel.org
Subject: Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

On Wed, Aug 22, 2012 at 06:00:54PM +0530, Naveen N. Rao wrote:
> The ACPI spec doesn't provide for a way for the bios to pass down
> recommended thresholds to the OS on a _per-bank_ basis. This patch adds
> a new boot option, which if passed, allows bios to initialize the CMCI
> threshold. In such a case, we simply skip programming any threshold
> value.
> 
> As fail-safe, we initialize threshold to 1 if some banks have not been
> initialized by the bios and warn the user.
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> ---
>  Documentation/x86/x86_64/boot-options.txt |    5 ++++
>  arch/x86/include/asm/mce.h                |    1 +
>  arch/x86/kernel/cpu/mcheck/mce.c          |    4 +++
>  arch/x86/kernel/cpu/mcheck/mce_intel.c    |   39 +++++++++++++++++++++++++++--
>  4 files changed, 46 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
> index c54b4f5..ec92540 100644
> --- a/Documentation/x86/x86_64/boot-options.txt
> +++ b/Documentation/x86/x86_64/boot-options.txt
> @@ -50,6 +50,11 @@ Machine check
>  		monarchtimeout:
>  		Sets the time in us to wait for other CPUs on machine checks. 0
>  		to disable.
> +   mce=bios_cmci_threshold
> +		Don't overwrite the bios-set CMCI threshold. This boot option
> +		prevents Linux from overwriting the CMCI threshold set by the
> +		bios. Without this option, Linux always sets the CMCI
> +		threshold to 1.
>  
>     nomce (for compatibility with i386): same as mce=off
>  
> diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
> index a3ac52b..8ad5078 100644
> --- a/arch/x86/include/asm/mce.h
> +++ b/arch/x86/include/asm/mce.h
> @@ -171,6 +171,7 @@ DECLARE_PER_CPU(struct device *, mce_device);
>  #ifdef CONFIG_X86_MCE_INTEL
>  extern int mce_cmci_disabled;
>  extern int mce_ignore_ce;
> +extern int mce_bios_cmci_threshold;
>  void mce_intel_feature_init(struct cpuinfo_x86 *c);
>  void cmci_clear(void);
>  void cmci_reenable(void);
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 292d025..401359d 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -82,6 +82,7 @@ static int			mce_panic_timeout	__read_mostly;
>  static int			mce_dont_log_ce		__read_mostly;
>  int				mce_cmci_disabled	__read_mostly;
>  int				mce_ignore_ce		__read_mostly;
> +int				mce_bios_cmci_threshold	__read_mostly;
>  int				mce_ser			__read_mostly;

AFAICT, this is actually a single-bit flag but we're using a whole
integer for it and from looking at the other boot options a couple of
them are used as flags too.

Care to define a

struct boot_flags {
	__u64 	mce_bios_cmci_threshold : 1,
		__reserved		: 63;
};

and use

	boot_flags.mce_bios_cmci_threshold

in the conditionals below instead?

I'll try to convert the rest of them to that struct and thus save some
more space...

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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